Timeout with withTimeout in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run a block with a timeout of 1000 milliseconds.

Kotlin

withTimeout([1]) {
    println("Running task")
}

Drag options to blanks, or click blank then click option'

A100

B5000

C1000

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using seconds instead of milliseconds.

Passing zero which means no timeout.

The withTimeout function takes the timeout duration in milliseconds. Here, 1000 means 1 second.

2fill in blank

medium

Complete the code to catch the timeout exception thrown by withTimeout.

Kotlin

try {
    withTimeout(500) {
        Thread.sleep(1000)
    }
} catch ([1]) {
    println("Timeout occurred")
}

Drag options to blanks, or click blank then click option'

ATimeoutCancellationException

BException()

CInterruptedException

DCancellationException

Attempts:

3 left

💡 Hint

Common Mistakes

Catching a generic Exception instead of the specific timeout exception.

Using InterruptedException which is unrelated here.

The withTimeout function throws TimeoutCancellationException when the timeout expires.

3fill in blank

hard

Fix the error in the code to properly use withTimeout in a suspend function.

Kotlin

suspend fun runTask() {
    withTimeout([1]) {
        delay(2000)
    }
}

Drag options to blanks, or click blank then click option'

Adelay(1000)

B1000L

C"1000"

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string instead of an integer.

Passing a Long literal which is allowed but not necessary here.

Passing a function call instead of a number.

The timeout duration must be an integer number of milliseconds. Using 1000 is correct. Quotes make it a string which is invalid.

4fill in blank

hard

Fill both blanks to create a map of words to their lengths only if length is greater than 3.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val lengths = words.filter { word -> [2] }.associate { word -> word to [1] }

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Aword.length

Blen(word)

Cword.length > 3

Dlen(word) > 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using Python syntax like len(word).

Using incorrect condition syntax.

In Kotlin, word.length gets the length of the string. The condition word.length > 3 filters words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths only if length is less than 5.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val result = words.filter { word -> [3] }.associate { word -> [1] to [2] }

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Aword.uppercase()

Bword.length

Cword.length < 5

Dword.toUpperCase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using deprecated toUpperCase() instead of uppercase().

Using Python syntax like len(word).

Incorrect condition operator.

Use word.uppercase() to convert to uppercase in Kotlin. word.length gets length. The condition word.length < 5 filters words shorter than 5.

Practice

1. What does the Kotlin function withTimeout do?

easy

A. It cancels all running coroutines immediately.

B. It repeats a block of code until a timeout occurs.

C. It stops a block of code if it runs longer than the specified time.

D. It delays the execution of a block for a fixed time.

Solution

1. Step 1: Understand the purpose of withTimeout

   withTimeout is designed to stop a block of code if it exceeds a given time limit.

2. Step 2: Compare options with the definition

   Only "It stops a block of code if it runs longer than the specified time." correctly describes this behavior. Other options describe different coroutine behaviors.

3. Final Answer:

   It stops a block of code if it runs longer than the specified time. -> Option C

4. Quick Check:

   withTimeout stops code after time limit [OK]

Hint: Remember: withTimeout interrupts long-running code [OK]

Common Mistakes:

• Confusing withTimeout with delay function
• Thinking it repeats code instead of stopping
• Assuming it cancels all coroutines globally

2. Which of the following is the correct syntax to use withTimeout in Kotlin?

easy

A. withTimeout(1000) { /* code block */ }

B. withTimeout { 1000, /* code block */ }

C. withTimeout[1000] { /* code block */ }

D. withTimeout: 1000 { /* code block */ }

Solution

1. Step 1: Recall the function signature

   The correct syntax uses parentheses with the timeout in milliseconds as the first argument, followed by a lambda block.

2. Step 2: Match options with correct syntax

   withTimeout(1000) { /* code block */ } matches this pattern exactly. Others use incorrect brackets or misplaced arguments.

3. Final Answer:

   withTimeout(1000) { /* code block */ } -> Option A

4. Quick Check:

   withTimeout uses parentheses for timeout [OK]

Hint: Use parentheses with timeout value before code block [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Placing timeout inside the block instead of argument
• Using colon instead of parentheses

3. What will be the output of this Kotlin code?

import kotlinx.coroutines.*

fun main() = runBlocking {
    try {
        withTimeout(100) {
            repeat(5) { i ->
                println("Processing $i")
                delay(50)
            }
        }
    } catch (e: TimeoutCancellationException) {
        println("Timeout occurred")
    }
}

medium

A. Processing 0
Processing 1
Processing 2
Processing 3
Processing 4

B. Processing 0
Processing 1
Timeout occurred

C. Timeout occurred

D. Processing 0
Timeout occurred
Processing 1

Solution

1. Step 1: Analyze the timing of the loop and timeout

   Each iteration delays 50ms. After two iterations, 100ms timeout is reached.

2. Step 2: Determine output before timeout

   "Processing 0" and "Processing 1" print before timeout triggers. Then exception is caught and "Timeout occurred" prints.

3. Final Answer:

   Processing 0 Processing 1 Timeout occurred -> Option B

4. Quick Check:

   Timeout stops after 2 prints + exception message [OK]

Hint: Multiply delay by iterations to compare with timeout [OK]

Common Mistakes:

• Assuming all iterations print before timeout
• Ignoring exception catch block
• Thinking timeout cancels immediately without partial output

4. Identify the error in this Kotlin code using withTimeout:

import kotlinx.coroutines.*

fun main() = runBlocking {
    withTimeout(100) {
        delay(200)
        println("Done")
    }
}

medium

A. TimeoutCancellationException is thrown because delay exceeds timeout.

B. Syntax error: withTimeout requires a try-catch block.

C. No error; code runs and prints "Done" after 200ms.

D. Delay function cannot be used inside withTimeout.

Solution

1. Step 1: Understand withTimeout behavior with delay

   The delay of 200ms exceeds the 100ms timeout, causing a TimeoutCancellationException.

2. Step 2: Check error handling

   No try-catch is present, so exception will be thrown and program will crash.

3. Final Answer:

   TimeoutCancellationException is thrown because delay exceeds timeout. -> Option A

4. Quick Check:

   Delay longer than timeout causes exception [OK]

Hint: Delay longer than timeout causes exception unless caught [OK]

Common Mistakes:

• Assuming code waits full delay then prints
• Thinking try-catch is mandatory syntax
• Believing delay can't be used inside withTimeout

5. You want to run a network request that should timeout after 500ms. Which Kotlin code correctly uses withTimeout to achieve this and handle timeout gracefully?

hard

A. try {
networkRequest()
withTimeout(500)
} catch (e: TimeoutCancellationException) {
println("Request timed out")
}

B. withTimeout(500) {
try {
networkRequest()
} catch (e: TimeoutCancellationException) {
println("Request timed out")
}
}

C. withTimeoutOrNull(500) {
networkRequest()
} ?: println("Request timed out")

D. try {
withTimeout(500) {
networkRequest()
}
} catch (e: TimeoutCancellationException) {
println("Request timed out")
}

Solution

1. Step 1: Understand correct placement of withTimeout and try-catch

   The timeout should wrap the networkRequest call, and the exception should be caught outside to handle timeout.

2. Step 2: Evaluate options for proper structure

   try { withTimeout(500) { networkRequest() } } catch (e: TimeoutCancellationException) { println("Request timed out") } correctly wraps networkRequest inside withTimeout and catches the exception outside. withTimeout(500) { try { networkRequest() } catch (e: TimeoutCancellationException) { println("Request timed out") } } catches inside, which won't catch timeout. withTimeoutOrNull(500) { networkRequest() } ?: println("Request timed out") uses withTimeoutOrNull (valid but different). try { networkRequest() withTimeout(500) } catch (e: TimeoutCancellationException) { println("Request timed out") } misplaces withTimeout after networkRequest.

3. Final Answer:

   try { withTimeout(500) { networkRequest() } } catch (e: TimeoutCancellationException) { println("Request timed out") } -> Option D

4. Quick Check:

   Wrap withTimeout around call, catch outside [OK]

Hint: Wrap withTimeout around call, catch exception outside [OK]

Common Mistakes:

• Catching exception inside withTimeout block
• Placing withTimeout after the call
• Confusing withTimeout with withTimeoutOrNull